CN101677215A - Switching power source device, switching power source control circuit, and switching power source device control method - Google Patents

Switching power source device, switching power source control circuit, and switching power source device control method Download PDF

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CN101677215A
CN101677215A CN200910168718A CN200910168718A CN101677215A CN 101677215 A CN101677215 A CN 101677215A CN 200910168718 A CN200910168718 A CN 200910168718A CN 200910168718 A CN200910168718 A CN 200910168718A CN 101677215 A CN101677215 A CN 101677215A
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switch element
conducting
main switch
moment
switching power
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CN101677215B (en
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陈建
园部孝二
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Fuji Electric Co Ltd
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Fuji Electric Device Technology Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)
  • Rectifiers (AREA)

Abstract

The present invention provides a switching power source device, a switching power source control circuit, and a switching power source device control method which can prevent reverse current in any operational mode, and further realize a stable synchronous rectification function. In maximum on width control circuits (4), the synchronization with an on timing of primary MOSFETs is the beginning forthe MOSFETs (served as synchronous rectification elements) to indicate the maximum on width, while a maximum on width signal Tmot2 which indicates the end of the maximum on width after a predetermined period is generated. In a synchronous control circuit (5), the on timing of Qs is determined by being synchronized with a later timing between the timing for indicating the beginning of the maximumon width and the on timing of an internal diodes detected based on a drain-to-source voltages Vds, and the off timing of Qs is determined by being synchronized with a earlier timing between the off timing of the primary MOSFETs and the timing for indicating the end of the maximum on width.

Description

The control method of switching power unit, switching power source control circuit and switching power unit
Technical field
The invention provides the control method of the switching power unit, switching power source control circuit and the switching power unit that possess series resonant circuit, especially relate to the control method of switching power unit, switching power source control circuit and the switching power unit of elimination adverse current of electric current when underload with current resonance inductor and current resonance capacitor.
Background technology
As the switching power unit of prior art, be well known that the device that possesses the current resonance code converter as shown in Figure 5.In this current resonance code converter, input direct voltage Vi is applied in the series resonant circuit with resonant inductor Lr and resonant capacitor Cr, 2 main switch element Qa, Qb by formations such as MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) are turn-offed in conducting, be controlled at the path of the primary side current that circulates among the first coil L1 of the transformer T that power converter uses, thus the sinuous electric current of circulation in the first coil L1 of transformer T.In addition, be connected with the rectifier diode D1, the D2 that secondary current I1, the I2 that is responded to are carried out rectification respectively at the second coil L2, the tertiary coil L3 of transformer T (coil that makes L1: L2: L3 is than being n: 1: 1); With will be to the output voltage V of load LD 0Level and smooth output capacitor C 0And, to the output voltage V of load LD 0Feed back to the drive circuit 3 of main switch element Qa, Qb by error amplifier 1 and VCO (voltage control oscillating circuit) 2, control flows is led to electric current and the voltage of the first coil L1 of transformer T, with output voltage V 0Be controlled to be constant voltage.In addition, VCO2 brings into play function in such a way, if that is: be judged as output voltage V 0 than setting voltage height according to the output of error amplifier 1, perhaps being judged as is underload, then improves its output frequency; If it is lower than setting voltage to be judged as output voltage V 0, perhaps being judged as is heavy duty, then reduces its output frequency.
But, under the situation of switching power unit that so constitutes as the power supply use of low-voltage and high-current, when secondary current I1, I2 circulate in rectifier diode D1, the D2 of the secondary side setting of transformer T, because the forward drop V of rectifier diode D1, D2 F, produce bigger power loss V F* I 0I0 is any one of secondary current I1, I2.Therefore, as shown in Figure 6, replace these rectifier diodes D1, D2, and use the switch element that respectively that conducting resistance is lower MOSFETQs1, Qs2 use as synchronous rectification and connect and carry out synchronous rectification, reduce the current resonance circuit of the separate excitation type of drive of the power loss that so produces.The MOSFETQs1 of Fig. 6, Qs2 be switched on shutoff control synchronously respectively with the main switch element Qa of primary side, the operating frequency fop that the Qb conducting is turn-offed by drive circuit 3, thereby secondary current I1, I2 are put aside at capacitor C alternately 0
The switching power unit of the prior art that constitutes like this, according to making main switch element Qa, Qb switch motion, the mode that the transformer T that uses by voltage transformation obtains direct current output arbitrarily constitutes, thereby depends on that the size etc. of the load LD that is connected with secondary side puts aside at capacitor C 0Electric charge by the electric current (reverse current) of discharge generation to transformer T side adverse current, appear at the power loss problem in the adverse current zone.
Fig. 7 is the circuit diagram of an example of the current resonance code converter of expression secondary side diode rectification.In this Fig. 7, the transformer T of the current resonance code converter of Fig. 5 is divided into magnetizing inductance composition Lm and ideal transformer Ti illustrates, be convenient to express its operating principle with understanding.At this, before the explanation of the power loss in above-mentioned adverse current zone, describe for the operating principle of current resonance code converter.
In current resonance code converter shown in Figure 7, can define two kinds of following basic anti-resonant frequencies.Represent the inductance of resonant inductor Lr, the magnetizing inductance composition of transformer T and the electric capacity of resonant capacitor Cr respectively at this Lr, Lm and Cr.
[formula 1]
fr 1 = 1 2 π Lr · Cr . . . ( 1 )
[formula 2]
fr 2 = 1 2 π ( Lr + Lm ) · Cr . . . ( 2 )
In the switching power unit of Fig. 5, Fig. 7, under the situation of the supply that load LD is had electric power, the voltage of the magnetizing inductance composition Lm of transformer T according to output voltage V 0 by clamper (clamp) to n * (V 0+ V F), magnetizing inductance composition Lm does not participate in current resonance, moves with the first resonance frequency fr1 (with reference to above-mentioned (1) formula) by resonant capacitor Cr and resonant inductor Lr decision, thus to secondary side circuit supply capability.In this case, electric current I m that in magnetizing inductance composition Lm, circulates and resonance electric current I r and, as flowing to the charging and discharging currents of resonant capacitor Cr.At this moment, about the operating frequency fop of main switch element Qa, Qb, control so that output voltage V by VCO2 0Stable.
The second resonance frequency fr2, be that load LD to the secondary side that is connected in transformer T does not carry out the resonance frequency under the situation that electric power supplies with, since ideal transformer Ti not as the voltage of the magnetizing inductance composition Lm of transformer performance functional transformer T not by clamper, so mainly resonant inductance Lr and the magnetizing inductance composition Lm of capacitor C r, the resonant inductor Lr by resonant capacitor Cr carry out the resonance action.
Concrete resonance action for the current resonance code converter of Fig. 7, can according to its operating frequency fop and the first resonance frequency fr1 (below, abbreviate resonance frequency as) relation, the size of the load LD that is connected with secondary side at transformer T is divided into 6 pattern (Mode1～Mode6) consider as shown in Figure 8.
That is, Mode1～Mode3 is the operating frequency fop situation lower than resonance frequency fr1 in Fig. 8, and Mode4～Mode6 is that operating frequency fop equates with resonance frequency fr1 or the situation higher than resonance frequency fr1.In addition, with respect to the nominal load (maximum load) of switching power unit if the size of connected load LD is more than 50% the load condition of attaching most importance to (HL:HeavyLoad), if be 50～20% then for light-load state (LL:Light Load), 20% be extra-light loading state (VLL:Very Light Load) with next if be.
At first, for the pattern of the current resonance code converter of Fig. 5, utilize action waveforms shown in Figure 9 to describe.
In Fig. 9, represent, operating frequency fop (with 1 cycle of switch motion as Top) lower than resonance frequency fr1 (is Tr with at this moment harmonic period), and the attach most importance to action waveforms of first pattern (Mode1) of load condition of load LD.At this, moment s1 after the main switch element Qa conducting that is right after a side (below, so-called sj (j=1～16) constantly is not meant moment but uses as the zone with width) beginning is divided into an action cycle Top 10 operate conditions (s1～s10) describe constantly successively.
In Fig. 9, (A), (B) is grid voltage Vga, the Vgb as main switch element Qa, the Qb of the output of drive circuit 3, (C), (D) is electric current I a, the Ib that circulates in main switch element Qa, Qb, (E) be the voltage between terminals Vc of resonant capacitor Cr, (F), (G) be electric current I 1, the I2 that circulates in rectifier diode D1, D2.
Figure 10 is the circuit diagram of operate condition of the moment s1 of expression first pattern.At this, be after being right after main switch element Qa conducting, and inherit the result of the action of moment s10 formerly that at this moment electric current I a circulates along direction shown in the arrow.And another main switch element Qb turn-offs.At this moment, circulation and the reciprocal exciting current Im of resonance current Ir in magnetizing inductance composition Lm are because it is bigger than resonance current Ir, so electric current circulates as discharging current in the direction of the charge discharge of resonant capacitor Cr.Based on the resonance current Ir of the resonant circuit of primary side by ideal transformer Ti at the sensed electric current of the second coil L2, be fed into load LD from rectifier diode D1.
In the operate condition of moment s2 shown in Figure 11, continuing is that main switch element Qa is conducting, and Qb is for turn-offing.But the same direction circulation of exciting current Im that circulates in reverse direction with resonance current Ir and resonance current Ir before begins resonant capacitor Cr is charged.With previous moment s1 similarly,, by the ideal transformer Ti sine-wave current I1 (with reference to Fig. 9 (F)) that in the rectifier diode D1 of secondary side, circulates load LD is powered based on the resonance current Ir of the resonant circuit of primary side.
At moment s3 shown in Figure 12, continue is that main switch element Qa is conducting, the state of Qb for turn-offing, but process was become from the primary side of ideal transformer Ti secondary side is not carried out the electric power supply by the half period (Tr/2) of the harmonic period Tr of the size decision of resonant inductor Lr and resonant capacitor Cr.But because operating frequency fop is lower than resonance frequency fr1, main switch element Qa is a conducting state, so the resonant circuit of primary side at the second above-mentioned resonance frequency fr2 resonance takes place, resonant capacitor Cr is recharged by exciting current Im.Because it is very long that the cycle of the second resonance frequency fr2 was compared with the cycle of the first resonance frequency fr1, so the harmonic wave of s3 is almost straight line constantly.
Moment s4 as shown in figure 13, being equivalent to 2 main switch element Qa, Qb all becomes the Dead Time of shutoff (dead time).At this, distributed capacitance C_Qb for the main switch element Qb of the distributed capacitance C_Qa of the main switch element Qa of off state and the opposing party's off state, along direction circulating current Ia and Ib shown in the arrow of Figure 13, the both end voltage of 2 distributed capacitance C_Qa, C-Qb is changed respectively.At this moment, resonant capacitor Cr and 2 distributed capacitance C_Qa, C_Qb constitute the resonant circuit of resonant inductor Lr and magnetizing inductance composition Lm, and so that the mode of resonant capacitor Cr charging is carried out the resonance action, electric power does not supply to secondary side from primary side.In addition, because the electric capacity of capacity ratio distributed capacitance C_Qa, the C_Qb of resonant capacitor Cr is a lot of greatly, so in moment s4, resonant capacitance Cr also can be counted as constant pressure source.
At moment s5 shown in Figure 14, continuing is that 2 main switch element Qa, Qb are in off state, big in the both end voltage change of moment s4 distributed capacitance C_Qb, in Figure 13, if the side that is connected with resonant capacitance Cr of distributed capacitance C_Qb as reference potential, then becomes big at the negative voltage absolute value.Consequently, become conducting state at its body diode of main switch element Qb (body-diode) D_Qb.At this moment, carry out resonance at primary side by resonant circuit, begin primary side from ideal transformer Ti through tertiary coil L3 circulating current I2, beginning is to load LD supply capability.That is, exciting current Im that in magnetizing inductance composition Lm, circulates and resonance current Ir in reverse direction, and as the current flowing bigger than resonance current Ir, so resonant capacitor Cr continues to be recharged.In addition, because current Ib circulates in body diode D_Qb (electric current be oriented direction shown in the arrow), the opposing party's main switch element Qa is turned off, therefore the terminal of the side that is connected with resonant capacitor Cr of the first coil L1 of transformer T becomes high-voltage side, and the terminal of an opposite side becomes low voltage side.
At moment s6 shown in Figure 15, be to be right after main switch element Qb conducting state afterwards, current Ib still circulates along direction shown in the arrow therein.And another main switch element Qa turn-offs.Therefore, terminal with side resonant capacitor Cr connection the first coil L1 of transformer T becomes high-voltage side (terminal of an opposite side becomes low voltage side), pass through ideal transformer Ti at the sensed electric power of tertiary coil L3 from the resonant circuit of primary side, be fed into load LD from rectifier diode D2.At this moment, circulation and the reciprocal exciting current Im of resonance current Ir in magnetizing inductance composition Lm, and it is bigger than resonance current Ir, so resonant capacitor Cr is recharged based on spill current (Im-Ir).
At moment s7 shown in Figure 16, continuing is that main switch Qa turn-offs the state of Qb conducting.But, exciting current Im becomes littler than resonance current Ir, and the exciting current Im that circulates in the other direction with resonance current Ir becomes with the same direction of resonance current Ir and circulates (direction shown in the arrow among Figure 16) before, and savings begins to be discharged at the electric charge of resonant capacitor Cr.So, pass through ideal transformer Ti to the rectifier diode D2 of secondary side circulation sine-wave current (with reference to Fig. 9 (G)), to load LD supply capability from the resonant circuit of primary side.
At moment s8 shown in Figure 17, continuing is that main switch Qa turn-offs the state of Qb conducting.The resonance release of half period among resonant inductor Lr and the resonant capacitor Cr becomes from primary side to secondary side supply capability not.In addition, when resonant capacitor Cr continued discharge, the resonant circuit of primary side carried out the resonance action with the second above-mentioned resonance frequency fr2.
Moment s9 shown in Figure 180 is equivalent to the Dead Time that 2 main switch element Qa, Qb are shutoff.At this, the distributed capacitance C_Qb for the distributed capacitance C_Qa of main switch element Qa and the opposing party's main switch element Qb respectively along direction circulating current Ia and Ib shown in the arrow of Figure 18, changes the both end voltage of 2 distributed capacitance C_Qa, C_Qb.At this moment, resonant capacitor Cr and 2 distributed capacitance C_Qa, C_Qb constitute the resonant circuit of resonant inductor Lr and magnetizing inductance composition Lm, and so that the mode of resonant capacitor Cr discharge is carried out the resonance action, but electric power is not supplied to secondary side from primary side.In addition, because the electric capacity of capacity ratio distributed capacitance C_Qa, the C_Qb of resonant capacitor Cr is a lot of greatly, so, can regard resonant capacitor Cr as constant pressure source at moment s9.
At moment s10 shown in Figure 19, continuing is 2 main switch element Qa, the Qb state for turn-offing, but in the big result of both end voltage change of moment s9 distributed capacitance C_Qa is, in its body diode of main switch element Qa D_Qa conducting.At this moment, carry out resonance at primary side by resonant circuit, by the second coil L2 electric current I 1 that goes into circulation, beginning is supplied with to the electric power of load LD from the primary side of ideal transformer Ti.In addition, exciting current Im that in magnetizing inductance composition Lm, circulates and resonance current Ir opposite direction, and as the current flowing bigger than resonance current Ir, resonant capacitor Cr is further discharged.
Figure 20 is the electric current, the movement oscillogram of voltage waveform of each one of second pattern of expression current resonance code converter.At this, fop is lower than resonance frequency fr1 for operating frequency, and load is that second pattern (Mode2) of light-load state describes.
Shown in Figure 20 (A), (B), the Dead Time of regulation is set in grid voltage Vga, the Vgb of main switch element Qa, Qb.In addition, owing to be light-load state, so the electric current I a that circulates in main switch element Qa, Qb, Ib diminish, the voltage between terminals Vc amplitude of fluctuation of the resonant capacitor Cr shown in this figure (E) also diminishes.In addition, do not have great changes when exciting current Im and heavy duty, so the influence of exciting current Im becomes relatively greatly, phase place is leading during than heavy duty.Below, only the different operate condition of circuit operation for heavy duty shown in Figure 9 the time describes.
In Figure 21, expression is right after the operate condition of the moment s11 after the main switch element Qa conducting.This state is the state that main switch element Qa conducting, Qb turn-off, resonant capacitor Cr constitutes the resonant circuit of resonant inductor Lr and magnetizing inductance composition Lm, different with the moment s1 (with reference to Figure 10) among the Mode1 shown in Figure 9, (Figure 21+side become hot side) is lower because the both end voltage of magnetizing inductance composition Lm, though main switch element Qa conducting can not be immediately from primary side to the secondary side supply capability.
After this, resonant capacitor Cr its voltage between terminals Vc that discharges reduces, last when satisfy following formula (3) at moment s11, beginning resonance moves in the resonant circuit of the primary side in above-mentioned moment s1, from primary side to the secondary side supply capability.At this, Vf is the rectifier diode D1 of secondary side, the forward voltage of D2.
(Vi-Vc)*Lm/(Lr+Lm)＝n*(V 0+Vf)
……(3)
Represent among Figure 22 that through half period (Top/2) of switch motion, 2 main switch element Qa, Qb are the operate condition of moment s12 of the Dead Time of shutoff.In this case, the body diode D_Qb conducting of main switch element Qb, beginning exciting current Im (exactly, being the resonance current of the resonant circuit that is made of resonant capacitor Cr, resonant inductor Lr and magnetizing inductance composition Lm) from previous moment s4 is continuously introduced among the resonant capacitor Cr.But (Figure 22+side become hot side) deficiency is therefore different with operate condition (s5 constantly) shown in Figure 14 because the both end voltage of magnetizing inductance composition Lm, can not be to the secondary side supply capability.
Figure 23 represents next operate condition of s13 constantly.As shown here, main switch element Qb conducting, resonant capacitor Cr constitutes the resonant circuit with resonant inductance Lr and magnetizing inductance composition Lm.But it is different with the situation of the moment s6 of first pattern (Mode1) shown in Figure 9, (Figure 23+side become hot side) is lower because the both end voltage of magnetizing inductance composition Lm, though main switch element Qb conducting can not be immediately from primary side to the secondary side supply capability.
After this, resonant capacitor Cr is recharged, when its voltage between terminals Vc satisfies the operate condition (state of the moment s6 of Figure 15) of following formula (4), the resonance action by resonant inductance Lr and resonant capacitor Cr, from primary side to the secondary side supply capability.
Vc*Lm/(Lr+Lm)＝n*(V 0+Vf)
……(4)
After this, advance to s7, s8 constantly from moment s6, when becoming the moment s9 that 2 main switch element Qa, Qb all turn-off, distributed capacitance C_Qb for the distributed capacitance C_Qa of main switch element Qa and the opposing party's main switch element Qb, along direction circulating current Ia and the Ib shown in the arrow of Figure 18, the both end voltage of 2 distributed capacitance C_Qa, C_Qb is changed respectively.At this moment, because load LD is a light-load state, as shown in figure 24 at the moment s14 of the body diode D_Qa of main switch element Qa conducting, (Figure 24+side become hot side) deficiency because the both end voltage of magnetizing inductance composition Lm, different with operate condition (s10 constantly) shown in Figure 19, can not be to the secondary side supply capability.
Then, fop is lower than resonance frequency fr1 for operating frequency, and the 3rd pattern (Mode3) of littler extra-light loading (VLL) state of load LD describes.Figure 25 is the electric current, the movement oscillogram of voltage waveform of each one of the 3rd pattern of expression current resonance code converter.In this case, resonance current Ir further diminishes, and the amplitude of fluctuation of the voltage between terminals Vc of resonant capacitor Cr also further diminishes.The voltage Vc of resonant capacitor Cr arrange by exciting current Im (perhaps, the resonance current of the resonant circuit that constitutes by resonant capacitor Cr, resonant inductor Lr, magnetizing inductance composition Lm), its phase place is further leading.
In moment s2, as above-mentioned resonance current Ir shown in Figure 11 and exciting current Im circulation, but resonance current Ir much smaller than exciting current Im, the voltage between terminals Vc of resonant capacitor Cr is arranged by exciting current Im.Therefore, shorten based on the time of discharging and recharging from the resonance current Ir of resonant inductor Lr.Therefore, in becoming the 3rd pattern (Mode3) of extra-light loading, use the state of transferring to moment s3 than first pattern (heavy duty Mode1), short time of second pattern (underloaded Mode2).
Similarly, at moment s7, become little more than exciting current Im as above-mentioned resonance current Ir shown in Figure 16, the voltage between terminals Vc of resonant capacitor Cr is arranged by exciting current Im.Therefore, shorten based on the time of discharging and recharging, in the pattern (Mode3) of extra-light loading, transfer to the operate condition of s8 constantly during than heavy duty, during underload quickly from the resonance current Ir of resonant inductor Lr.
And then, for the 4th to the 6th pattern (Mode4～6) under the operating frequency fop situation high or more equal, in Figure 26, Figure 29 and Figure 30, represent its action waveforms respectively than resonance frequency fr1.
Figure 26 is the electric current, the movement oscillogram of voltage waveform of each one of the 4th pattern of expression current resonance code converter.The 4th pattern (Mode4) is that operating frequency fop is more than the resonance frequency fr1, and load LD is heavy duty state.
Figure 27 represents among Figure 26 the operate condition of the moment s15 that 2 main switch element Qa, Qb turn-off simultaneously.Under the situation of the 4th pattern (Mode4), even turn-off at moment s15 main switch element Qa, the body diode D_Qb conducting of main switch element Qb continues the discharge of the energy of savings in resonant inductor Lr, magnetizing inductance composition Lm+the side current potential kept.Therefore, resonance current Ir circulates in ideal transformer Ti, and electric power is supplied to secondary side from primary side.In this case, because resonant inductor Lr is applied in voltage (n * (V 0+ V F)+V C+ V F) become the situation that is similar to constant voltage discharge, so the electric current I 1 that circulation roughly reduces point-blank in rectifier diode D1.At ensuing moment s5, resonance current Ir circulates in reverse direction and go into circulation sine-wave current I2 in the rectifier diode D2 of secondary side.Therefore, sine-wave current I1, the I2 that becomes in the 4th pattern at secondary side circulates continuously.
In Figure 28, expression is the operate condition of the moment s16 that turn-offs simultaneously of 2 main switch element Qa, Qb similarly.In this case, even main switch element Qb turn-offs, the body diode D_Qa of main switch element Qa becomes conducting.In addition, by the discharge of resonant inductor Lr, magnetizing inductance composition Lm+the side current potential kept, and electric power is fed into secondary side.
Figure 29 is the electric current, the movement oscillogram of voltage waveform of each one of the 5th pattern of expression current resonance code converter.At this, be more than the resonance frequency fr1 for operating frequency fop, and load LD is that the 5th pattern (Mode5) of light-load state describes.
Being right after 2 main switch element Qa, Qb moment s15, the s16 after turn-offing simultaneously, can feed electrical power to secondary side respectively.But because load LD is a light-load state, at moment s11 and s12 and s13 and s14 thereafter, same with second pattern (with reference to Figure 20), becoming respectively can not be to the state of secondary side supply capability.
Figure 30 is the electric current, the movement oscillogram of voltage waveform of each one of the 6th pattern of expression current resonance code converter.At operating frequency fop is more than the resonance frequency fr1, and is among the Mode6 of extra-light loading (VLL) state, 2 main switch element Qa, Qb respectively conducting during, occur secondary side not moment s11 and s3 and the s13 and the s8 of supply capability.
More than, resonance action for 6 patterns of current resonance code converter shown in Figure 7 is illustrated, below, for rectifier diode D1, D2 with secondary side be replaced into the lower MOSFETQs1 of conducting resistance, the separate excitation of current resonance code converter of Fig. 6 behind the Qs2 drives synchronous rectification and investigates.
In the synchronous rectification mode, self-excitation type of drive and separate excitation type of drive are arranged.For the separate excitation type of drive,, when built-in logic circuit in power supply IC, can easily realize synchronous rectification for power supply manufacturer in order to use the logical circuit output drive signal.Therefore, each company of IC manufacturer has designed various separate excitation type of drive (with reference to patent documentation 1～5 described later).
Drive synchronous rectification if merely consider separate excitation, can think generally that then the synchronized signal of MOSFETQs1, Qs2 and the signal of main switch element Qa, Qb being carried out switch control get final product synchronously.But, in fact, if in each pattern, do not detect the adverse current zone respectively and be transformed to synchronous with it respectively drive signal, then put aside electric charge at output capacitor C0 by the electric current (reverse current) of discharge generation to transformer T side adverse current, efficient occurs and reduce, and then because electric current might cause the generation of circuit damage to the primary side adverse current.
At this, adverse current zone in each pattern, it is relation by the operating frequency fop and the resonance frequency fr1 of current resonance code converter, and the zone of load LD decision, wherein operating frequency fop changes according to circuit parameter and load condition, and resonance frequency fr1 is by the size decision of resonant capacitor Cr and resonant inductor Lr.Therefore, be simple method though make the synchronous synchronous rectification of synchronized signal and power switch signal, need to be used to eliminate the countermeasure in 5 following adverse current zones in this case.
Promptly, by signal Vga, Vgb the switching power unit of supplying with secondary current I1, I2 is turn-offed in 2 main switch element Qa, Qb conducting respectively, in first pattern (Mode1) as shown in figure 31, in later half moment s3 and s8 of the half period of switch motion shown in Figure 9 (Top/2), by turn-offing MOSFETQs1, the Qs2 that Synchronization Control is used reliably, can stop secondary current I1, I2 adverse current respectively.Therefore,, signal Vga, the Vgb shown in this figure (A), (B) output to MOSFETQs1, the Qs2 that Synchronization Control is used, then at this adverse current electric current that circulates in the zone (RangeA) of s3 and s8 constantly as synchronized signal Vgs1, Vgs2 if maintaining the original state.
In addition, different with the RangeA that causes adverse current under the situation of second pattern (Mode2), the zone of the RangeB that represents in Figure 32 (being equivalent to moment s11 and s13 shown in Figure 20) also might cause adverse current.
Similarly, under the situation of the 3rd pattern (Mode3), as shown in figure 33, in RangeA and RangeB, cause on the basis of adverse current, also cause adverse current at RangeC (it is equivalent in the half period of harmonic period Tr but zone that resonance finishes).
Under the situation of the 4th pattern (Mode4) shown in Figure 34, so because secondary current I1, I2 needn't worry to cause adverse current continuously.
In the 5th pattern (Mode5) shown in Figure 35, in the zone (being equivalent to moment s11 and s13 shown in Figure 29) of RangeD, cause adverse current.
Under the situation of the 6th pattern (Mode6), as shown in figure 36, not only in RangeD, cause adverse current, in the zone (being equivalent to moment s3 and s8 shown in Figure 30) of RangeE, also cause adverse current.Therefore, synchronized signal Vgs1, Vgs2 as the MOSFETQs1 that uses for Synchronization Control, Qs2, under the situation of suitable and the signal (same signal) that signal Vga, Vgb are synchronous, owing in each pattern 1～5 and 5,6, adverse current takes place, be necessary that therefore (Vgs1 among the RangeA～E), the signal waveform of Vgs2 are formed separately with the zone corresponding with them.
Therefore, in the switching power unit of prior art, the CWP generative circuit is set, this CWP generative circuit with signal Vga, Vgb conduction period slightly narrower pulse duration export constant pulse width signal (CWP:Constant Width Pulse), synchronized signal Vgs1, Vgs2 are carried out waveform shaping.Promptly, identical with resonance frequency fr1 or at operating frequency fop than under its high situation, make synchronized signal Vgs1, Vgs2 and signal Vga, Vgb synchronous, when operating frequency fop than resonance frequency fr1 hour, make synchronized signal Vgs1, Vgs2 and the same EOS of constant pulse width signal CWP (for example with reference to patent documentation 1).Thus, even be replaced at rectifier diode D1, D2 under the situation of the lower MOSFETQs1 of resistance, Qs2, also can prevent adverse current electric current from secondary side with secondary side.
But, in the invention of patent documentation 1 record, because the moment of the rising of synchronized signal Vgs1, Vgs2 is always synchronous with signal Vga, Vgb, therefore as the adverse current zone (RangeB) in second pattern (Mode2), be difficult to prevent be right after the adverse current of secondary circuit before going into circulation.In addition, under or the situation identical with resonance frequency fr1 than its high Mode4～Mode6 at operating frequency fop, if synchronized signal Vgs1, Vgs2 and signal Vga, Vgb are synchronous, then can not stop the adverse current under light-load state (LL), extra-light loading state (VLL).
As other switching power unit, consider the method (for example, with reference to patent documentation 2) of the synchronous rectification of formation shown in Figure 37 (A) with the control circuit of MOSFET.In addition, the action waveforms of its each one of expression in Figure 37 (B).The drain source voltage across poles (Vds (on)) of the switch element of synchronous rectification being used with comparator 51 (MOSFET) compares with reference voltage REF and detects the conducting of synchronous rectification with MOSFET or its body diode, only detect this conducting and signal Vgp be H (High) during, synchronous rectification provided with MODFET make the signal of synchronous rectification with the MOSFET conducting.Promptly, by with (AND: logic product) circuit 430 generate the comparison signal Vdsc of the output of device 510 as a comparison and primary side main switch element Qa, Qb signal Vgp's and signal, with it as being outputed to MOSFETQs1, Qs2 by the synchronized signal Vgs of waveform shaping (that is, Vgs1, Vgs2) as switch element.
Usually the drain source voltage across poles Vds of MOSFET turn-offs at MOSFET under the state of circulating current in body diode, becomes body diode forward drop V FIf (with the source potential is reference potential, then is accurately-V F).On the other hand, under the state of MOSFET conducting, become the product of the electric current of its conducting resistance and circulation, its value (absolute value) is usually than V FLittle.Above-mentioned reference voltage REF, its absolute value is taken as quite little value, allow the conducting of MOSFET so that can detect to the electric current that in body diode, circulates at first, even diminishing, MOSFET conducting afterwards and drain source voltage across poles Vds also can make MOSFET continue conducting (in fact, consider noise etc., need this value is increased to the degree that can be error-free the conducting of MOSFET or its body diode be detected).But shown in Figure 37 (B), when secondary current Is reduces when becoming zero, no matter how little the value of reference voltage REF is, and it is littler that the product of the conducting resistance of MOSFET and the electric current of circulation can become eventually.Thus, comparison signal Vdsc upset, MOSFET turn-offs, and becomes the state of circulating current in body diode, and drain source voltage across poles Vds becomes-V FThus, the comparison signal Vdsc MOSFET conducting once more of overturning once more, consequently comparison signal Vdsc overturns again.After, as shown in the zone errors of Figure 37 (B), become fully till zero up to secondary current Is, carry out to high-frequency the conducting of MOSFET repeatedly and turn-off.This oscillatory occurences is more remarkable when load lightens secondary current Is reduction.Like this, the invention of record in patent documentation 1, owing to when secondary current Is minimizing becomes zero, must carry out the vibration of high frequency repeatedly, so become the mode that has problem from the viewpoint of noise and power converter efficient.
Set conduction threshold (V as the conducting voltage of considering diode-built-in TH2) invention, the invention of record is arranged in the patent documentation 3.At this, only determine constantly owing to make the conducting of synchronized signal, so exist in the problem that the Dead Time of signal Vga, the Vgb setting to primary side causes misoperation easily by the conducting voltage of diode-built-in.In addition, because decision conducting threshold value (V constantly TH1) be-small voltage value about 20mV and be negative value, therefore be subjected to The noise easily, there is the moment of the turn-offing action problem of unstable that becomes.
In other switching power unit, the resonance current by current transformer detection primary side detects exciting current by the secondary side ancillary coil, and resonance current detection signal and exciting current detection signal are compared in addition.Based on detecting the signal whether this compare result signal, power switch signal and resonance current detection signal surpass 0A, generate synchronous rectification signal (for example, with reference to patent documentation 4).
In the technology of this patent documentation 4, can solve the reflux problem in each discontinuous mode, but use the backward constantly thereby electrical efficiency reduction of conducting of MOSFET in the pattern (Mode1,4) under the heavy duty state owing to synchronous rectification.And owing to utilize current transformer and ancillary coil circuit structure to become complicated etc. in testing circuit, it is very difficult to be designed to best adjusted value, not preferred from the viewpoint of cost.
In addition, as realizing that the circuit of synchronous rectification and the current transformation that can stop electric current to circulate lose the power converter of reduction, have the invention of record in patent documentation 5 in the other direction.This invention is, utilizes relatively voltage between the source drain of synchronous rectification transistor of comparator circuit, by switch element it stoped when detecting in the other direction electric current.At this, determined to make the moment of synchronous rectification transistor shutoff, but for not record of the moment that makes its conducting.Therefore, the countermeasure as the adverse current (RangeB, D) that prevents electric current is ineffective in above-mentioned second pattern (Mode2), the 3rd pattern (Mode3), the 5th pattern (Mode5) and the 6th pattern (Mode6).
No. 7184280 specification of [patent documentation 1] United States Patent (USP)
No. 2008/0055942 specification of [patent documentation 2] U.S. Patent Application Publication
No. 2005/0122753 specification of [patent documentation 3] U.S. Patent Application Publication
[patent documentation 4] spy opens the 2005-198438 specification
[patent documentation 5] spy opens the 2005-198375 specification
Summary of the invention
Like this in the switching power unit of prior art, do not possess in whole above-mentioned 6 patterns (with reference to Fig. 8) and all prevent the drive circuit of secondary current reliably to the adverse current of primary side.Especially, need be by preventing the electric current adverse current under the light-load state, and synchronous rectification is stably detected it with the drain source voltage across poles (Vds) of MOSFET, enforcement can prevent the simple synchronous rectification of misoperation.
The present invention finishes in view of the above problems, its objective is to be provided at the adverse current that can both prevent electric current in the pattern arbitrarily, realizes the control method of switching power unit, switching power source control circuit and the switching power unit of stable synchronous rectification.
In the present invention,, provide series resonant circuit is applied input direct voltage, produce the output voltage of stipulating by transformer, the switching power unit of load supply capability in order to address the above problem.
In this switching power unit, series resonant circuit has current resonance inductor and current resonance capacitor.And a plurality of main switch elements or main switch element group for example are made of MOSFET, and alternately the current path that switches series resonant circuit is turn-offed in conducting.Transformer, by primary side to main switch element or main switch element group carry out conducting turn-off control from the series resonance electric current to the secondary side induced current.A plurality of synchronous rectification switch elements, diode-built-in is connected in parallel, correspondingly with any one of a plurality of main switch elements or main switch element group respectively carries out the secondary current that conducting turn-offs transformer and carries out rectification.Maximum conducting width control circuit is indicated the beginning of maximum conducting width to synchronous rectification with switch element synchronously constantly with the conducting of main switch element or main switch element group, and is indicated the end of maximum conducting width at the appointed time.Synchronization control circuit, control described synchronous rectification in the following manner and use the conduction period of switch element, that is: indicate with maximum conducting width control circuit moment of the beginning of maximum conducting width, perhaps conducting any one slower moment constantly of the diode-built-in that is detected with the voltage between terminals signal of switch element according to synchronous rectification is synchronous, make synchronous rectification switch element conducting, and, with the shutoff moment of main switch element or main switch element group, perhaps maximum conducting width control circuit indicates any one moment early in the moment of end of maximum conducting width synchronous, and synchronous rectification is turn-offed with switch element.
Adopt the control method of switching power unit of the present invention, switching power source control circuit and switching power unit, utilization is applied to the gate turn-on cut-off signals and the maximum conducting width signal of the grid of main switch element or main switch element group, control synchronous rectification is with conduction period of switch element, therefore can get rid of whole noises beyond main switch element or main switch element consist of time of conducting.
In addition, conducting voltage by the diode that is connected in parallel with switch element with the voltage between terminals level detection of switch element and synchronous rectification according to synchronous rectification, it only is used for the moment control of synchronous rectification with the conducting of switch element, use maximum conducting width signal effectively, can provide realization not to be subjected to that the detection noise of voltage level between terminal is that influence, no misoperation, control method, switching power source control circuit and the switching power unit of the switching power unit of the synchronous rectification of the current resonance code converter that can not cause adverse current.
Description of drawings
Fig. 1 is the integrally-built circuit diagram of the switching power unit of expression execution mode.
Fig. 2 is the maximum conducting width control circuit of expression switching power unit and the circuit diagram of synchronization control circuit.
Fig. 3 is the sequential chart of the control action of the secondary side current that carries out of the synchronization control circuit of key diagram 2.
Fig. 4 is the integrally-built circuit diagram of the switching power unit of expression bridge-type.
Fig. 5 is the circuit diagram of an example of the existing current resonance code converter of expression.
Fig. 6 is the figure that expression is replaced into the rectifier diode of Fig. 5 the current resonance code converter of MOSFET.
Fig. 7 is the circuit diagram of an example of the current resonance code converter of expression secondary side diode rectification.
Fig. 8 is operating frequency fs and the relation of resonance frequency fr and the figure of load condition of 6 patterns of expression.
Fig. 9 is the electric current of each one in first pattern of expression current resonance code converter, the movement oscillogram of voltage waveform.
Figure 10 is the circuit diagram of operate condition of the moment s1 of expression first pattern.
Figure 11 is the circuit diagram of operate condition of the moment s2 of expression first pattern.
Figure 12 is the circuit diagram of operate condition of the moment s3 of expression first pattern.
Figure 13 is the circuit diagram of operate condition of the moment s4 of expression first pattern.
Figure 14 is the circuit diagram of operate condition of the moment s5 of expression first pattern.
Figure 15 is the circuit diagram of operate condition of the moment s6 of expression first pattern.
Figure 16 is the circuit diagram of operate condition of the moment s7 of expression first pattern.
Figure 17 is the circuit diagram of operate condition of the moment s8 of expression first pattern.
Figure 18 is the circuit diagram of operate condition of the moment s9 of expression first pattern.
Figure 19 is the circuit diagram of operate condition of the moment s10 of expression first pattern.
Figure 20 is the movement oscillogram of the current/voltage of each one in second pattern of expression current resonance code converter.
Figure 21 is the circuit diagram of operate condition of the moment s11 of expression second pattern.
Figure 22 is the circuit diagram of operate condition of the moment s12 of expression second pattern.
Figure 23 is the circuit diagram of operate condition of the moment s13 of expression second pattern.
Figure 24 is the circuit diagram of operate condition of the moment s14 of expression second pattern.
Figure 25 is the electric current of each one in the 3rd pattern of expression current resonance code converter, the movement oscillogram of voltage waveform.
Figure 26 is the electric current of each one in the 4th pattern of expression current resonance code converter, the movement oscillogram of voltage waveform.
Figure 27 is the circuit diagram of operate condition of the moment s15 of expression the 4th pattern.
Figure 28 is the circuit diagram of operate condition of the moment s16 of expression the 4th pattern.
Figure 29 is the electric current of each one in the 5th pattern of expression current resonance code converter, the movement oscillogram of voltage waveform.
Figure 30 is the electric current of each one in the 6th pattern of expression current resonance code converter, the movement oscillogram of voltage waveform.
Figure 31 is the figure that passes through the current waveform of the sensed secondary side of transformer when being illustrated in first pattern.
Figure 32 is the figure that passes through the current waveform of the sensed secondary side of transformer when being illustrated in second pattern.
Figure 33 is the figure that passes through the current waveform of the sensed secondary side of transformer when being illustrated in the 3rd pattern.
Figure 34 is the figure that passes through the current waveform of the sensed secondary side of transformer when being illustrated in the 4th pattern.
Figure 35 is the figure that passes through the current waveform of the sensed secondary side of transformer when being illustrated in the 5th pattern.
Figure 36 is the figure that passes through the current waveform of the sensed secondary side of transformer when being illustrated in first pattern.
Figure 37 is the figure that is used to illustrate prior art problems, (A) is the figure of expression synchronous rectification with the control circuit of MOSFET, (B) is the movement oscillogram of each one of control circuit.
Symbol description
1 error amplifier
2VCO (voltage control oscillating circuit)
3 drive circuits
4,41,42 maximum conducting width control circuits
5,51,52 synchronization control circuits
The Lr resonant inductor
The Cr resonant capacitor
Qa, Qb, Qa1, Qa2, Qb1, Qb2MOSFET (main switch element)
The T transformer
C 0Output capacitor
The Ld load
Qs, Qs1, Qs2MOSFET (synchronous rectification switch element)
The Ds diode-built-in
Embodiment
Below, describe for embodiments of the present invention with reference to accompanying drawing.Fig. 1 is the integrally-built circuit diagram of the switching power unit of expression execution mode.
This switching power unit constitutes in such a way, that is: input direct voltage Vi is applied to the series resonant circuit with resonant inductor Lr and resonant capacitor Cr, load LD is produced the output voltage V of regulation by transformer T 0In addition, except that transformer T, also inductance can be set, with leakage inductance as circuit resonance inductor Lr.External inductance perhaps is set, by the synthetic formation current resonance inductor Lr of this external inductance and leakage inductance except that transformer T.MOSFETQa, Qb are for alternately carrying out the main switch element of switch switching to the circuit pathways of series resonant circuit by the primary side at transformer T.The end of resonant inductor Lr is connected with the end of the first coil L1 of transformer T, and the other end of the first coil L1 is connected with the end of resonant capacitor Cr.
At the secondary side of transformer T, the second coil L2 and tertiary coil L3 are connected in series with each other, its tie point and output capacitor C 0Be connected with the end of load LD.In addition, the other end of the second coil L2 and tertiary coil L3 is respectively by MOSFETQs1, Qs2 and output capacitor C 0Be connected with the other end of the ground connection side of load LD.MOSFETQs1, Qs2 will turn-off from the sensed secondary current I1 of transformer T, I2 conducting by the action corresponding to MOSFETQa, Qb, load LD is supplied with the synchronous rectification switch element of the output voltage V 0 of regulation, they are connected in parallel with hereinafter described diode-built-in (body diode, perhaps body diode and external diode) Ds respectively.
Output voltage V to load LD supply 0, feed back to the drive circuit 3 of MOSFETQa, Qb by error amplifier 1 and VCO (voltage control oscillating circuit) 2.At this moment, alternately produce signal Vga, the Vgb that carries out the conducting shutoff in the moment of regulation at drive circuit 3, control the moment that makes in regulation makes MOSFETQa, Qb along the direction of arrow electric current I a, Ib circulation, electric current and the voltage that circulates among the first coil L1 of control transformer T thus is with the output voltage V of secondary side 0Be controlled to be constant voltage.In addition, VCO2 brings into play function in such a way, according to the output of error amplifier 1, is judged as output voltage V that is: 0Than setting voltage height, when perhaps being judged as underload, improve its output frequency, be judged as output voltage V 0Lower than setting voltage, when perhaps being judged as heavy duty, reduce its output frequency.
In maximum conducting width control circuit 41,42, synchronous constantly with the conducting of MOSFETQa, Qb, the MOSFETQs1, the Qs2 that use for synchronous rectification, the maximum conducting width of the stipulated time that indication is turn-offed MOSFETQs1, Qs2 when leaving during this period forcibly, generate for this reason output become maximum conducting width during the maximum conducting width signal Tmot of H (in addition during be L (Low)), perhaps as the maximum conducting width end signal Tmot2 of the signal of the end of the maximum conducting width of indication.In addition, the beginning of maximum conducting width, indicated by signal Vga, Vgb for MOSFETQa, Qb, it is identical with the moment of MOSFETQa, Qb conducting that signal Vga, Vgb become H.And, the MOSFETQs1 that actual generation synchronous rectification is used, the synchronized signal Vgs1 of Qs2, the synchronization control circuit 51 of Vgs2, in 52, make MOSFETQs1, the moment of Qs2 conducting, with the moment (being maximum conducting width signal Tmot becomes H from L the moment) of the beginning of indicating maximum conducting width, perhaps according to MOSFETQs1, the drain source voltage across poles Vds1 of Qs2, the conducting of the detected diode-built-in Ds of Vds2 any one slower moment is constantly determined synchronously, and make MOSFETQs1, the moment that Qs2 turn-offs, with MOSFETQa, the shutoff of Qb perhaps indicates any one moment early in the moment of the end of maximum conducting width to determine synchronously constantly.
Then, the control circuit (switching power source control circuit) for switching power unit shown in Figure 1 describes.
Fig. 2 is the maximum conducting width control circuit of expression switching power unit and the circuit diagram of synchronization control circuit.At this, synchronization control circuit 5 is represented any one of synchronization control circuit 51 or 52 and is expressed.In addition, about maximum conducting width control circuit 41,42, by they being used the one-shot multivibrator of adjusting its pulse duration by the external parts that are connected with the MOT terminal constitute, can realize the execution mode of the maximum conducting width signal Tmot of maximum conducting width control circuit 41,42 outputs, with it as first embodiment.But, because one-shot multivibrator itself is known, so omit more detailed explanation about first embodiment.At this, carry out describing according to second embodiment that the maximum conducting width control circuit 4 of the action of first embodiment is realized for utilization.In addition, maximum conducting width control circuit 4 shown in Figure 2 is represented any one of maximum conducting width control circuit 41 or 42 and is expressed.In addition, under the situation that realizes maximum conducting width control circuit 41,42 with one-shot multivibrator, also can use identical synchronization control circuit 5.In addition, (in Fig. 2, note is made Ls in the second coil L2 of the secondary side of control transformer T or any one of tertiary coil L3.) the MOSFETQs that uses of the synchronous rectification of secondary current Is in, the diode Ds that is built between its drain-source is connected in parallel.
Maximum conducting width control circuit 4, possesses the signal input terminal 4a that is supplied to from the signal Vga of drive circuit shown in Figure 13, any one of Vgb (following note is simply made signal Vgp), with the MOT terminal 4b that external parts were connected of the size that is used to adjust maximum conducting width (be equivalent to use under the situation of one-shot multivibrator, as the pulse duration of the maximum conducting width signal Tmot of the output of one-shot multivibrator).This maximum conducting width control circuit 4 is not exported maximum conducting width signal Tmot itself, but the circuit of the maximum conducting width end signal Tmot2 of the finish time of the maximum conducting width of output expression.Maximum conducting width control circuit 4, by the inverter 43 that is connected with signal input terminal 4a, the constant current source 44 that is connected with supply voltage VDD, an end be connected capacitor C1 that the other end is grounded with constant current source 44, discharging and recharging of this capacitor C1 controlled the switch S 1 of conductings shutoff by inverter 43 and the comparator 45 that will compare charging voltage and the reference voltage REF1 of capacitor C1 constitutes in order to control.
In this maximum conducting width control circuit 4, when turn-offing, begin capacitor C1 is charged from the electric current of constant current source 44 according to the signal Vgp switch S 1 of signal input terminal 4a.And, surpass moment at the voltage of the reversed input terminal (-) of comparator 45 to the reference voltage REF1 of non-inverting input (+), the maximum conducting width end signal Tmot2 of the output of device 45 is L (Low) from H (High) upset as a comparison, and the end of maximum conducting width is communicated to synchronization control circuit 5.When maximum conducting width end signal Tmot2 became L, the output with non-(NAND: with non-) circuit 54 of synchronization control circuit 5 became H circuits for triggering 55 is resetted.Afterwards, when based on 1 conducting of signal Vgp switch S, the capacitor C1 maximum conducting width end signal Tmot2 that discharged becomes H.In addition, the moment that begins to become H of maximum as mentioned above conducting width signal Tmot for signal Vgp, signal Vgp is imported into the NAND circuit 54 of the reseting terminal that is connected circuits for triggering 55, and the maximum conducting width control circuit 4 of embodiment 2 can be indicated the beginning (end that reset of circuits for triggering 55) of maximum conducting width thus.Therefore, in embodiment 2, about the beginning and the end of maximum conducting width, can indicate the maximum identical moment of conducting width signal Tmot under the situation with the one-shot multivibrator that uses embodiment 1, can set maximum conducting width thus with best conducting width.
Output time at the maximum conducting width end signal Tmot2 that is used for exporting from comparator 45 is fit to the MOT terminal 4b that resonance frequency fr1 adjusts, and connects resistance or capacitor etc.Connecting under the situation of resistance, be divided to this resistance, can postpone the output time of maximum conducting width end signal Tmot2 according to the resistance value of resistance from the electric current of constant current source 44.In addition, under the situation that connects capacitor, be equal to greatly mutually, can postpone the output time of maximum conducting width end signal Tmot2 thus with the capacitance change of capacitor C1.
At this, because signal Vgp and maximum conducting width end signal Tmot2 obtain logic product (it " non-") by NAND circuit 54, so finish to become in the conduction period that maximum conducting width end signal Tmot2 becomes the moment of L and signal Vgp L the moment, any one side early, circuits for triggering 55 are resetted.
Synchronization control circuit 5, possess and when going out extra-light loading, be supplied to the signal input terminal 5a that becomes the extra-light loading of H status signal VLL by not shown electric circuit inspection, and be provided its drain source voltage across poles Vds from the MOSFETQs that synchronous rectification is used, also be provided from the maximum conducting width signal Tmot of maximum conducting width control circuit 4 outputs or maximum conducting width end signal Tmot2 with to MOSFETQa, Qb and carry out the signal Vgp that control is turn-offed in conducting, by the conduction period of output synchronized signal Vgs control MOSFETQs.This synchronization control circuit 5, by based on the comparator 53 of reference voltage REF2 according to drain source voltage across poles Vds output detection signal Vdsc, calculate maximum conducting width signal Tmot and NAND circuit 54 signal Vgp and non-signal, aaset bit terminal S provides the level detection signal Vdsc of comparator 53, provides circuits for triggering 55 NAND circuit 54 and non-signal to reseting terminal R, constituting of signal after reversing with the Q output signal that is transfused to these circuits for triggering 55 and the extra-light loading status signal VLL by inverter 56 near signal input terminal 5a with circuit 57.
In this synchronization control circuit 5, the reversed input terminal (-) of comparator 53 is grounded by Zener diode ZD, and is connected with supply voltage VDD by resistance R 1, and also the drain terminal of the MOSFETQs that uses by resistance R 2 and synchronous rectification is connected.The reference voltage REF2 of comparator 53 is provided for non-inverting input (+).
At this, supply voltage VDD note is made A, when threshold voltage (Vds_th) note of the drain source voltage across poles Vds of the MOSFETQs during with the level detection signal Vdsc of the output of device 53 as a comparison upset was made X, 2 of comparator 53 inputs equated during Vds=X, so following formula is set up.In addition, above-mentioned threshold voltage (Vds_th) is the different value of threshold value of turn-offing with the conducting that relates to MOSFETQs.
(A-X)*(R2/(R1+R2))+X＝REF2
∴(A-X)+X*(1+R1/R2)＝REF2*(1+R1/R2)
∴X*(R1/R2)＝(1+R1/R2)*REF2-A
The threshold voltage (Vds_th) of the drain source voltage across poles of the MOSFETQs when therefore, level detection signal Vdsc overturns
Vds _ th = - VDD R 2 R 1 + REF 2 ( 1 + R 2 R 1 ) . . . ( 5 )
When drain source voltage across poles Vds surpasses (Vds_th) (strictly speaking, both be negative value, when the absolute value of Vds is bigger than the absolute value of (Vds_th)), the level detection signal Vdsc of the output of device 53 is H from the L upset as a comparison.That is, between drain-source not under the state of circulating current, the value of drain source voltage across poles Vds is for just, and level detection signal Vdsc becomes L.The level detection signal Vdsc of this drain source voltage across poles Vds is provided as the asserts signal of circuits for triggering 55, on the other hand, be transfused to the output signal of NAND circuit 54 of signal Vgp and maximum conducting width signal Tmot or maximum conducting width end signal Tmot2 as the reset signal of circuits for triggering 55.In addition, the Q output signal of circuits for triggering 55 is provided for NAND circuit 57 with the reverse signal from the extra-light loading status signal VLL of inverter 56 output, and its output signal is used as the gate drive signal Vgs of the MOSFETQs that synchronous rectification uses.Circuits for triggering 55 are for resetting preferential circuit.That is, even drain source voltage across poles Vds surpasses (Vds_th), if signal Vgp then can not carry out set to circuits for triggering 55 for the state of the L before the beginning of the maximum conducting width of indication.Thus, the Dead Time that can prevent from signal Vga, Vgb, the to set misoperation that might take place to primary side.
Then, the control method for switching power unit describes.
Fig. 3 is the sequential chart of the control action of the secondary side current that carries out of the synchronization control circuit of key diagram 2.At this, describe for the situation that realizes maximum conducting width control circuit 41,42 by one-shot multivibrator.In Fig. 3 (A), will arrange expression about 6 pattern Mode1～6 along same time shaft from the signal Vgp of drive circuit shown in Figure 13.Fig. 3 (B) is the secondary current Is that circulates among the MOSFETQs that synchronous rectification is used, the absolute value of the drain source voltage across poles of the MOSFETQs when removing level detection signal Vdsc upset with conducting resistance Ron with MOSFETQs (| Vds_th|) be converted into the figure that compares behind the electric current and represent.In addition, about threshold voltage Vds_th, can utilize above-mentioned formula (5) to calculate.Perhaps, can determine voltage Vds_th earlier, utilize formula (5) to adjust other parameter.
The waveform of expression level detection signal Vdsc among Fig. 3 (C).Shown in Fig. 3 (B) | Vds_th|/Ron, expression becomes the level of the secondary current Is of H from the level detection signal Vdsc of comparator 53 outputs.In addition, Fig. 3 (D) is maximum conducting width signal Tmot, and Fig. 3 (E) is extra-light loading status signal VLL, and Fig. 3 (F) is the synchronized signal Vgs from synchronization control circuit 5 outputs.
In first pattern (Mode1), any one moment early in the moment of turn-offing with the moment and the maximum conducting width signal Tmot of indication of the conducting of signal Vgp is synchronous, and synchronized signal Vgs turn-offs MOSFETQs.Therefore, the adverse current among the RangeA that can prevent from reliably in the prior art in later half moment half period of switch motion (Top/2), to take place.
In the pattern the second and the 5th (Mode2,5), with moment of indication maximum conducting width signal Tmot conducting and synchronous according to conducting any one slower moment constantly of the detected diode-built-in Ds of level detection signal Vdsc of drain source voltage across poles Vds, synchronized signal Vgs makes the MOSFETQs conducting, can prevent reliably in the prior art in the RangeB (Figure 32) of preceding half moment generation of the half period of switch motion (Top/2) or the adverse current among the RangeD (Figure 35).In addition, in case MOSFETQs becomes after the conducting, then the change of drain source voltage across poles Vds is ignored.Therefore, can not occur in see in the structure of patent documentation 2, whenever secondary current Is reduces when becoming zero the phenomenon of high-frequency vibration repeatedly.
In addition, owing to detect the extra-light loading state of load LD according to extra-light loading status signal VLL, so in the 3rd and the 6th pattern (Mode3,6), do not export synchronized signal Vgs from synchronization control circuit 5.Therefore, not conducting of MOSFETQs under the extra-light loading state can prevent the RangeC (Figure 33) of prior art or the adverse current of the middle generation of RangeE (Figure 36) reliably.About extra-light loading status signal VLL, the load LD that is defined herein as actual connection is a situation below 20% with respect to the nominal load (maximum load) of switching power unit, but the setting of this ratio can suitably be changed.
More than, because synchronized signal Vgs can be provided at the MOSFETQs that the moment shown in Figure 3 is used synchronous rectification, thereby under any one situation of first to the 6th pattern, adverse current can not take place can realize stable synchronous rectification.
In the above-described embodiment, be illustrated, but the present invention and also can be suitable in the control method of the switching power unit of bridge-type at the switching power unit or the switching power source control circuit of bridge-type for the switching power unit of semi-bridge type.
Fig. 4 is the integrally-built circuit diagram of the switching power unit of expression bridge-type.
In the switching power unit of the bridge-type of representing among Fig. 4, generate signal Vga, the Vgb that alternately carries out the conducting shutoff by drive circuit 3 in the moment of regulation, the MOSFETQb1 of the MOSFETQa1 of the first main switch element group, Qa2 and the second main switch element group, Qb2 at the primary side of transformer T based on signal Vga, Vgb switch alternately.Circulate along the direction of arrow at the MOSFETQa1 of the first main switch element group, the moment electric current I a of Qa2 conducting, circulate along the direction of arrow in the MOSFETQb1 of the second main switch element group, the moment current Ib of Qb2 conducting, respectively the series resonant circuit with resonant inductor Lr and resonant capacitor Cr is applied input direct voltage Vi.
Secondary side at transformer T, as MOSFETQs1, the Qs2 of synchronous rectification with switch element, to turn-off from the sensed secondary current I1 of transformer T, I2 conducting by action, load LD be supplied with the output voltage V of regulation corresponding to MODFETQb1, the Qb2 of MOSFETQa1, the Qa2 of the first main switch element group or the second main switch element group 0
At maximum conducting width control circuit 41, in 42, for with the MOSFETQa1 of the first main switch element group or the second main switch element group, Qa2, Qb1, the conducting of Qb2 synchronously constantly, the MOSFETQs1 that uses for synchronous rectification, Qs2, indication forces to turn-off MOSFETQs1 when leaving during this period, the maximum conducting width of the stipulated time of Qs2, generate output become maximum conducting width during the maximum conducting width signal Tomt of H (in addition during be L (Low)), perhaps as the maximum conducting width end signal Tmot2 of signal of the end of the maximum conducting width of indication.At this also be, the beginning of maximum conducting width, indicated by signal Vga, Vgb for MOSFETQa1, Qa2, Qb1, Qb2, signal Vga, Vgb become H, and the moment of MOSFETQa1, Qa2, Qb1, Qb2 conducting is identical.And, generate the MOSFETQs1 that synchronous rectification is used actually, the synchronized signal Vgs1 of Qs2, the synchronization control circuit 51 of Vgs2, in 52, make MOSFETQs1, the moment of Qs2 conducting, with the moment (being maximum conducting width signal Tmot becomes H from L the moment) of the beginning of indicating maximum conducting width, perhaps according to MOSFETQs1, the drain source voltage across poles Vds1 of Qs2, the conducting of the diode-built-in Ds that Vds2 detected any one slower moment is constantly determined synchronously, and make MOSFETQs1, the moment that Qs2 turn-offs is with MOSFETQa1, Qa2, Qb1, the shutoff of Qb2 constantly, perhaps indicate any one moment early in the moment of the end of maximum conducting width to determine synchronously.
In addition, identical about switching voltage control circuit and control method thereof with the situation of the switching power unit of semi-bridge type, thereby omit its explanation.

Claims (11)

1. switching power unit, it is that input direct voltage is applied to series resonant circuit, produces the output voltage of regulation through transformer, and the switching power unit that electric power is supplied with is carried out in load, it is characterized in that, comprising:
Series resonant circuit with current resonance inductor and current resonance capacitor;
Alternately a plurality of main switch elements or the main switch element group of the current path that switches described series resonant circuit turn-offed in conducting;
Control described main switch element or main switch element group by turn-offing in the primary side conducting, from described series resonant circuit at the faradic transformer of secondary side;
A plurality of synchronous rectification switch elements, its diode-built-in connects in parallel, correspondingly with any one of described a plurality of main switch elements or main switch element group respectively carries out conducting and turn-offs the in addition rectification of the secondary current of described transformer;
Maximum conducting width control circuit, indicate synchronously for the beginning of described synchronous rectification constantly with the conducting of described main switch element or main switch element group, and indicate the end of described maximum conducting width at the appointed time with the maximum conducting width of switch element; With
Synchronization control circuit, control described synchronous rectification in the following manner and use the conduction period of switch element, that is: indicate with described maximum conducting width control circuit moment of the beginning of described maximum conducting width, perhaps conducting any one slower moment constantly of the described diode-built-in that goes out with the voltage between terminals input of switch element according to described synchronous rectification is synchronous, make described synchronous rectification switch element conducting, and, with the shutoff moment of described main switch element or main switch element group, perhaps described maximum conducting width control circuit indicates any one moment early in the moment of end of described maximum conducting width synchronous, and described synchronous rectification is turn-offed with switch element.
2. switching power unit as claimed in claim 1 is characterized in that:
Described series resonant circuit, the leakage inductance by described transformer constitutes described current resonance inductance or its part.
3. switching power unit as claimed in claim 1 is characterized in that:
Described main switch element or main switch element group, formation make described series resonant circuit switch motion produce the semi-bridge type of alternating current or the converter of bridge-type.
4. switching power unit as claimed in claim 1 is characterized in that:
In described synchronization control circuit, under the size of described load with respect to nominal load is situation below the certain ratio, make described synchronous rectification with not conducting of switch element.
5. switching power unit as claimed in claim 1 is characterized in that:
In described maximum conducting width control circuit, can realize the described stipulated time till change setting finishes from beginning to the indication of indicating described maximum conducting width.
6. switching power unit as claimed in claim 1 is characterized in that:
As described synchronous rectification switch element, use MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor: metal-oxide semiconductor fieldeffect transistor).
7. switching power unit as claimed in claim 6 is characterized in that:
Described diode-built-in is the parasitic diode of described MOSFET.
8. switching power source control circuit, it comprises: the series resonant circuit with current resonance inductor and current resonance capacitor; Alternately a plurality of main switch elements or the main switch element group of the current path that switches described series resonant circuit turn-offed in conducting; By turn-off described main switch element of control or main switch element group in the primary side conducting, from described series resonant circuit at the faradic transformer of secondary side; With a plurality of synchronous rectification switch elements, its diode-built-in connects in parallel, correspondingly with any one of described a plurality of main switch elements or main switch element group respectively carry out conducting and turn-off the in addition rectification of the secondary current of described transformer, described switching power source control circuit is characterised in that, comprising:
Maximum conducting width control circuit, the conducting of itself and described main switch element or main switch element group indication synchronously constantly is for the beginning of described synchronous rectification with the maximum conducting width of switch element, and indicate after at the appointed time described maximum conducting width end and
Synchronization control circuit, control described synchronous rectification in the following manner and use the conduction period of switch element, that is: indicate with described maximum conducting width control circuit moment of the beginning of described maximum conducting width, perhaps conducting any one slower moment constantly of the described diode-built-in that goes out with the voltage between terminals input of switch element according to described synchronous rectification is synchronous, make described synchronous rectification switch element conducting, and, with the shutoff moment of described main switch element or main switch element group, perhaps described maximum conducting width control circuit indicates any one moment early in the moment of end of described maximum conducting width synchronous, and described synchronous rectification is turn-offed with switch element.
9. switching power source control circuit as claimed in claim 8 is characterized in that:
Under the size of the load that is connected with described switching power unit with respect to nominal load is situation below the certain ratio, make described synchronous rectification with not conducting of switch element.
10. switching power source control circuit as claimed in claim 8 is characterized in that:
In described maximum conducting width control circuit, can realize the described stipulated time till change setting finishes from beginning to the indication of indicating described maximum conducting width.
11. the control method of a switching power unit, it is applied in the series resonant circuit with current resonance inductor and current resonance capacitor at input direct voltage, produces the output voltage of stipulating through transformer, under the situation to the load supply capability,
A plurality of main switch elements or main switch element group, alternately the current path that switches described series resonant circuit is turn-offed in conducting, and will be connected in parallel to a plurality of synchronous rectification switch elements of diode-built-in, correspondingly with any one of described a plurality of main switch elements or main switch element group respectively carry out conducting and turn-off the in addition rectification of the secondary current of described transformer, the control method of described switching power unit is characterised in that:
When controlling the conduction period of described synchronous rectification usefulness switch element by synchronization control circuit,
Constantly make synchronously with the conducting of described main switch element or main switch element group to begin, and make described maximum conducting width end at the appointed time with respect to the maximum conducting width of synchronous rectification with switch element,
Conducting any one slower moment constantly of the described diode-built-in that goes out with the voltage between terminals input of switch element with the moment that described maximum conducting width is begun or according to described synchronous rectification is synchronous, make described synchronous rectification switch element conducting, and, with the shutoff of described main switch element or main switch element group constantly or any one moment early in moment of finishing of described maximum conducting width synchronous, described synchronous rectification is turn-offed with switch element.
CN2009101687180A 2008-09-16 2009-09-07 Switching power source device, switching power source control circuit, and switching power source device control method Expired - Fee Related CN101677215B (en)

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